Process for fhotochemically producing printing forms



Patented Apr. 1931 UNITED STATES;

PATENTI' OFFICE v JULIUS BEKK, OF IBERLIN-STEGLITZ, GERMANY, ASSIGNOR TO THE FIRM DR. BEKK & KAULEN GHEMISCHE FABRIK G. M. B. 18., OF BERLIN-LICHTERFELDE, GERMANY PROCESS FOR PHOTOCHEMICALLY PRODUCING PRINTING FORMS Application filed January 18, 1929, Serial No. 333,526,. and in Great Britain December 3, 1928.

The process of producing photo-mechan ical printing forms, especially printing plates, by means of sensitive chromate-colloid layers is generally known. The printing with these plates or the like takes place by those parts of the metal plates which are laid free after exposing and developing. These so-called positive-copying-processes enable the production of printing plates by copying an original without first preparing a negative. The hitherto known processes for preparing such printing forms, which for instance are applied in offset printing and to which the process described hereafter is attached, either work in the way that, for instance after developing of the chromate-eolloid copy, the parts of the metal plate laid free by such development are freed from fat or are otherwise rendered adapt-.

able for taking on fat-colours, WllQl'C'HQOI the whole plate is covered with colour and subsequently the colour adhering to the chrov mate-colloid layer is removed by wiping or rubbing in the presence of. water, diluted acids, or the like. As experience has shown these processes answer the purpose only in copying from coarse originals, line drawings and in the most favourable case with originals of coarse screen. The reason for this is that the freeing from fat has to be very thorough if the colour layer adhering to the free metal arts of the plates should be able to stand'tlie subsequent rubbing 01f without getting damaged. A very thorough treatment with acids as used for removing the fat on the other hand penetrates easily the chromate-colloid layer and causes the settling of colour in these penetrated places. Thus the printing plates are soiled for printand can no more be cleansed. Another Ob]GCti0I1 is that the mechanical hurts of the fat colour-image, which are almost indispensable with the wiping or rubbing of the colour-layer make it impossible to produce finer copies.

The present invention renders possible the production of good copies from' originals with finest screen.- This is achieved by producing above the chromate-colloid copies a varnishor resin-layer soluble in spirits, said varnishor resin-layer being removed from the unexposed portions of the chromate col loid layer, the remaining portions of vthe varnish or resin layer perfectly resisting the treatment with acids and remaining unattaeked in the covering with fatty colour. After the production of the.thus obtained varnishor resin-layer, the parts of the plate or the likelaid free by the preceding development are etched whereupon the whole printing form is covered with fat colour and exposed to the action of spirit or'some other dissolving agent of such a kind, which does not act upon thefat colour but on the other hand dissolves the varnish layer underneath, thus removing the connection between the respective places of the base and the fat colour, and thereby also removing the latter from those portionsof the plate which bear the hardened chromatelayer.

It is possible to use with advantage in this connection also an alkaline means, for instance on alkaline lye, by which the resinor varnish-layer as well as the colloid layer is rcmoved from the exposed places without the laid free metal being attacked or cerroded. Most suitable for this purpose is a mixture of alkaline lye and alkaline carbonate, which besides contains alkaline chromate and 'gelatinesolution. In this case also with quick work and in the application of a fairly concentrated lye a deteriorating influence of partsof the etching agent, which may have penetrated before in the colloid layer, on the metal lying-underncath this layer is prevented.

In order that the present invention may be better understood reference is made to the accompanying drawing wherein Figure 1 is a diagrammatic-elevation in section on an enlarged scale of a metal plate covered with a sensitive layer;

Fig. 2 is av corresponding view showing the same sensitive plate under the action of luminous rays;

Fig. 3 shows the plate exposed before, covered with a resin or varnish layer;

Fig. 4 shows the plate accordin to Fig. 3 after the removal ofthe soft, un ardened loci " Fig. 5 shows the plate according to Fig.

4 after being etched; n

Fig. 6 shows the plate according to Fig. 5 wholly covered with fat color which will be in a thicker layer on the free,etched portions of the plate than on the others; i Fig. 7 shows the plate according to Fig. 6 after the removal of the varnish or resin together with the fat color which was situ-' ated above said varnish or resin; 7

Fig. 8 shows the plate according to Fig. 7 after the removal of the hardened sensitive layer.

The preparing of the varnishor resinpicture or layer soluble in'spirit'may take place in the following manner.

iodine in potassium iodide to the etchi g agent in order to clean the metal and inft 'ease its taking capacity for fat colour.

For instance there can be used for the obtained etching means can be applied ac- Y cording to requirements upwards to several minutes on the printing form provided with the varnishor. resin-picture. After the etching the whole or plate is covered with fat colour and can printing form The sensitive chromate-colloid layer is put hereafter be treated with a spirit bath which on the clean grained metal plate or the like, does not attack the fat colour whereas the the chromate-colloid picture or image then varnishor resin-layer underlying it at the being. producedby exposure in the usual'place of the hardened colloid layer is disway. Before, however, developing this picsolved, the connection between the respecture with water, it; is rubbed with a resin tive portions of this colloid layer and the fat solution, e. g. with sandarac dissolved in colour thereby being removed, the spirit amyl acetate, the plate finally being watered penetrating, the fat color layer which con-.

under the sprinkler. By this treatment sists of solid color, and dissolving the resin those parts ofthe resin layer which are lying or varnish lying under the color particles.

venting with security the penetrating of the of fat colour. oosened from their base are on the unexposed portions of the chromate- It is to be noted in this connection that a fatcolloid layer are washed. away with the --color when rubbed on the plate will remain latter; I only in a thin layer on those portions which The varnish or resin-picture thus proare covered by varnish-or resin, but in a thick duced now'is treated with "a corrosive 6r layer on the laid free and etched deepened etching means for the laid 0 en portions portions of the plate. By then putting the of the metal, the varnish or re' n layer preplate under water sprinkler the particles etching means to the exposed portions of removed the metal plate and an'even slight corrosion ,thermeclianical ac tion.- Only in case where of these portions of the plate. By, the etchthe fat colour has been put on very thick a ing process the-grain is removed fro parts of the metal plate which hav been. be advisable for accomplishing the developlaid free before and the said part's .of'the ing process- The explanation for this is plate are somewhat deepened out. that in the deep laying places of the screen For the etching purpose different means picture the colour particles loosened from can be used as for instance acids or salt solu-- their basis are clutched sideways and hold tions or mixtures thereof, as in particular 'by those particles which are settled-on the -mixtures of different metal chlorides. Lacetched free parts of the metal plate.

tic acid or a mixture of aluminium chloride In place of or besides the spirit bath there and iron chloride may for instance be emcan also l'be' used a-treatment with alkaline .ployed. Very goodresults, however, are to lye, for instance caustic soda lye, by which be attained with a mixture of viron chloride the varnishor resin-layer as-well as the and nitric acid. 'The iron chloride herein hardened colloid'layer lying underneath said preferably-is used in a highly concentrated resin layer is removed without the laid free .form of solution byeither dissolving same, metal being attacked. -With special advanin a small quantity of water or mixing. it in tage there can be used for instance a caustic the solid state with the nitric acid. 4 In the soda lye with an addition of carbonate of application of such a viscous or paste like sodium and of alkaline bichromate and'gelaetching means those portions of the plate (tine. For preparing this means for instance which are covered by the chromate-colloid 200' gr. caustic soda, 100 r. crystallized solayer and by the varnishor resin-picture dium carbonate and 5 gr. jchromate of am- ;remain unattacked whereas the etching on monia are dissolved "in one liter of water to laid free lution. By applying such'a means the colloid as well as the-varnishor resin-layer is generally without requiring furarts of the metal is performed which is added 50 gr. of a 20% gelatine soa quite uni ormly and can be adjusted in depth at will. 65 There can also be added some solution of removed from the exposed places of the 1 of a colloid layer sensib e to light, which printing form orplate without the laid free metal being attacked.

Having now particularly described and ascertained the nature of my said invention, I declare that what I claim is:

l. A process for the photochemical production of metal printing forms by means of a colloid layer sensible to light, which comprises covering a base of metal with a light sensitive colloid layer, copying the original on said layer by means of a screen, covering the exposed sensitive layer with a protecting varnish-like layer, developing the exposed sensitive layer by means of water, thereby washing away at the same time those parts of the protecting layer lying over the not lighted portions of the sensitive colloid layer, etching the laid free portions of the metal by chemical etching means, covering the whole printing form with fat colour, and finally treating said printing form with a solvent for the varnish-like layer, said fat colour covering thereby being removed with said varnish-like layer from those parts of the printing form which had not been etched before.

2. A process for the photochemical production of metal printin forms by means comprises covering a base of metal with a light sensitive colloid layer, "copying the original on said layer by means of a screen covering the exposed sensitive la er with a varnish-like layer not to be attac ed by the printing colour, developing the, exposed sensitive colloid layer by means of water, thereby also removing the varnish-like layer from those parts of the metal form'which were not exposed to light before, etching the laid free portions of the metal by a mixture of iron chloride and nitric acid, covering the whole printing form with fat colour,

and finally treating said printing form with a solvent for the varnish-like-layer, said fat colour coverin thereby being removed with said varnishm layer'from those parts of the printing form which had not been etched before.

3. A process for the photochemical pro duction of metal printin forms by means of a colloid layer sensib e to light, which comprises covering a base of metal with a light sensitive colloid layer, cop 'ng the original on said layer by means 0 a screen covering the exposed sensitive layer with a varnish-like layer not to be attacked by the 'printing colour, developing the' exposed sensitive colloid layer by means of water,

.th'ereby also removing the varnish like layer from those parts of the metal form which were not exposed to light before, etching the laid free portions .of the metal by a mixture of iron chloride, nitric acid and a solution of iodine in disolvedpotassium iodide, cov.

our and finally treating said printing form with a solvent for the varnish-like layer, said fat colour covering thereby being removed with' said varnish-like layer from those parts of the printing form which had not been etched before.

v4:. A process for the photochemical production of metal printing forms by means of a colloid layer sensible to light, which comprises covering a base of metal with a light sensitive colloid layer, copying'the original on said layer by means of a screen, covering the exposed sensitive layer with a protecting varnish-like layer, developing the exposed sensitive layer by means of water, thereby washing away at the same time those parts of the protecting layer lying over the not-lighted portions of the sensitive colloid layer, etching the laid free portions of the metal by a mlxture of a highly concentrated solution of iron chloride and z nitric acid,

.covering the whole printing form with fat colour, and .finally treating said printing form with a solvent for the varnish-like layer, said fat colour coverin thereby being removed with said varnish-like layer from those parts of the printing not been etched before.

form which had 5.- A process for the'photochemical proparts of the protecting layer lying over the not-lightedportions of the sensitive colloid layer, etching the laid free portions of the inetal by a mixture of iron chloride and nitric acid, a covering the whole printing form with fat colour, and finally treating .sa1d printing form with alkaline y e for removing the covering layers from the exposed portions of the printing form without attacln'ng the metal of the form.

6. A (processaccording to claim 4 characterize b p the use of a mixture of alkaline lye and a 'ali carbonate for removin the covering layers from the etched am? colored-in plate.

7 A recess according t claim 4 characterized y the use of a mixture of alkaline "lye, alkali .carbonate, alkali bichromate. andgelatine solution for removin' the covering ayers from the etched and co cred-in plate. In testimony whereof I have hereunto set my hand. i

ering the whole printing form with fat coli= DR. JULIUS,BEKK. 

